President Maithripala Sirisena had appealed to drivers, station masters and technical staff to end their industrial action to enable students to get to school.
More than 400,000 students aged around 15 are sitting the examinations, which began Tuesday, and the president's office said the transport difficulties would cause them severe stress.
1st ODI: Sri Lanka humble Kohli-less India
"Those who go on strike must realise the plight of the students sitting the exams today," one parent told the ITN television network. "Don't they have children of their own?"
But a trade union spokesperson said staff would not return to work until their demands for higher pay were met. And he condemned parliament for declaring railways an essential service, effectively making the strike illegal.
"We did not want to cause inconvenience to the students, but we are continuing the strike because the government slapped the essential services order against us," Janaka Fernando said. Sri Lanka's heavily state-subsidised railways transported 136 million passengers last year.
COMMENTS
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ